Add support for `remote` resource

Hi,

First let me tell you that this may be the project the Incus project I was waiting for... So keep up the good work ! 👏 💪

Disclaimer, I just discovered the project and haven't had time to play with it first hand.
But from reading the full (nice and good) documentation, one thing has struck me: the lonely imperative `incus remote add` command (for OCI containers) crying to be replaced by its declarative sibling!

Hardly waiting to give it an actual shot

Thanks for sharing your beautiful work

TY
J